1. Field of the Invention
This invention relates to a radiation image diagnostic apparatus for reproducing and displaying a radiation image of an object on a display means.
2. Description of the Prior Art
There have heretofore been used methods wherein an object is exposed to radiation such as X-rays to record a radiation image of the object, a radiation image signal representing the radiation image is obtained, various algorithms for image processing are carried out on the image signal, and the radiation image of the object is reproduced and displayed as a visible image on a display means.
When a stimulable phosphor is exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, it stores a part of the energy of the radiation. Then, when the stimulable phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the stimulable phosphor in proportion to the stored energy of the radiation. As disclosed in U.S. Pat. No. 4,258,264 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object such as the human body to have a radiation image of the object stored thereon, and is then scanned by stimulating rays such as a laser beam which cause the stimulable phosphor sheet to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, image processing is carried out on the electric image signal, and the radiation image of the object is reproduced as a visible image by use of the processed image signal on a recording medium such as a photographic film, a display means such as a cathode ray tube (CRT), or the like.
In general, with the aforesaid radiation image recording and reproducing system, a single image is displayed at one time in the course of reproducing and displaying the radiation image on the display means such as the CRT display device. Therefore, in the case where two radiation images are to be compared with each other for the viewing of the condition of progress of a disease, hard copies have heretofore been formed one by one and viewed.
In order to view and compare the hard copies, it is necessary to provide a reproduction means capable of forming the hard copies. In the case where the hard copies are unnecessary in ordinary operations and the reproduction means for the formation of the hard copies is provided only for the purpose of the viewing and comparison, the equipment cost becomes unnecessarily high. Also, in the case where the reproduction means for the formation of the hard copies is provided, it is often desired that images be viewed and compared simply even though the hard copies need not be specially formed for comparison. Specifically, comparison of an image related to current viewing, particularly diagnosis, with a past image of the same object as the object of said image related to current viewing, or with a standard image representing the standard condition of said image related to current viewing.
The term "standard condition" as used herein means, for example, the condition prior to pressing or the standard condition of deformation in the case where the condition of deformation in a specific machine part caused by the pressing is to be investigated by use of a radiation image, or the condition of a standard appearance of a specific disease in a radiation image in the case where the specific disease of a specific portion of the human body is to be investigated by use of a radiation image, or a plurality of standard conditions of deformation in respective steps of the aforesaid deformation or a plurality of standard conditions of the disease in respective steps of the aforesaid disease.
In this specification, each group classified in accordance with the machine part, the object portion or the name of disease or the like is referred to as "kind", and a plurality of standard change conditions with respect to the same kind, for example, a plurality of standard deformation steps of the machine part and steps of progress of the disease are referred to as "steps".